Sulfide stress cracking of high strength modified Cr-Mo steels
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I.
INTRODUCTION
SERVICE failures of low alloy steel pipes and tools in the oil industry have induced an important research eflbrt since the last world war. The purpose was to select more resistant steels and microstructures. This effort concerns the whole oil industry: prospecting, extraction, transport, and refining. For oil field applications, solutions could be found whenever the products (oil or gas) were extracted out of moderately deep and sour wells. The draining of these easily accessible wells forced the oil industry, in the last ten years, to develop the exploitation of deeper and sourer wells, particularly for natural gas extraction. Their depths increased thus from 4000 m to 7000 m and even 10,000 m, the H2S content from 15 pct to 30 pct, and the temperatures from 150 ~ to 250 ~ The sulfide stress cracking (SSC) probability increased consequently, and this limits severely the service strength of the low alloy steels used for casing, tubing, and tool joints. That is the reason why the need for new grades of low alloy steels, having high mechanical characteristics as well as a good SSC resistance, has grown recently. The general objectives of this research were therefore: 1. on the technological level, to select low alloy steels grades which fulfill these requirements; 2. on the scientific level, to improve the understanding of the interaction mechanism between hydrogen and microstructure. Previous work 2'3 has shown that near equilibrium structures present good resistance to hydrogen embrittlement. In particular, high temperature tempered martensitic structures are the most resistant in aqueous H2S media. 4
J. C. CHARBONNIER and H. MARGOT-MARETTE are with IRSID, 78105 Saint-Germain-en-Laye Cedex, France. A. M. BRASS is with Laboratoire de Metallurgie (Associ6 au CNRS no. 177), Universit6 Paris-Sud, 91405 Orsay, France. M. AUCOUTURIER, formerly with Laboratoire de Metallurgie (Associ~ au CNRS, no. 177), Universit6 Paris-Sud, 91405 Orsay, France, is now with CNRS, Laboratoire de Physique des Solides, 1 Place A. Briand, 92195 Meudon Cedex, France. Manuscript submitted January 17, 1984.
METALLURGICAL TRANSACTIONS A
Nevertheless, satisfactory mechanical properties can be maintained only by alloying with hardening elements. Among the possible hardening elements, molybdenum was chosen for the present work together with additions of vanadium and titanium to study their role in Cr-Mo steels. The Cr-Mo grade has been chosen for the following reasons: at present, these steels are used for the manufacturing of tool joints. Furthermore, the SSC behavior of various high strength steels in chloride environment has been studied in previous work 5 and, in particular, the quenched and tempered ICr-0.2Mo steel has been proved to show the best behavior for ultimate strength levels between 1100 MPa and 1400 MPa (used for the high strength bolts). Various works of the Climax Molybdenum Co. 6'v have shown the advantage of a Mo addition to AISI 4135 steels for a possible use in the exploitation of sour wells. These results
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